The present invention relates to a control system for an internal combustion engine having a valve operating characteristic varying mechanism for continuously varying an operating phase (valve timing) of intake valves and/or exhaust valves.
A control system for an internal combustion engine having a valve operating characteristic varying mechanism for continuously varying an operating phase of intake valves and/or exhaust valves is described in Japanese Patent Laid-open No. 2000-104571, for example. In the control system described in this publication, a cleaning operation is performed to remove foreign matter deposited to a hydraulic control valve for controlling a hydraulic pressure to be supplied to the valve operating characteristic varying mechanism. This cleaning operation is performed by alternately supplying a maximum current and a minimum current for driving the hydraulic control valve when a vehicle is decelerated by an engine brake or when the fuel supply to the engine is interrupted, to thereby operate the hydraulic control valve over all its operable range.
The above cleaning operation causes a large change in a valve overlap amount (a time period during which both the intake valve and the exhaust valve are open), so that an efficiency of the engine as a pump changes and a pressure in an intake pipe also changes. As a result, a feeling of deceleration of the vehicle changes even when the vehicle is decelerated by the engine brake, or when the fuel supply to the engine is interrupted, which often causes a strange feeling to a driver of the vehicle.